1. Field of the Invention
The invention is concerned with the manufacture of magnetic materials.
2. Description of the Prior Art
Magnetic alloys containing Fe, Cr, and Co have received considerable attention on account of potentially high values of magnetic coercivity, remanence, and energy product achievable in such alloys. When suitably processed and shaped, these alloys may be advantageously used, e.g., in the manufacture of relays, ringers, and electro-acoustic transducers such as loudspeakers and telephone receivers.
Use of Fe-Cr-Co alloys in preference, e.g., to Fe-Al-Ni-Co or Fe-Co-Mo alloys is further based on mechanical properties and, in particular, on low-temperature formability of the alloy in a suitably annealed condition. For example, alloys disclosed in U.S. Pat. No. 4,075,437, "Composition, Processing, and Devices Including Magnetic Alloy", issued Feb. 21, 1978 may be shaped, e.g., by cold deformation into telephone receiver magnets whose design is disclosed in the paper by E. E. Mott and R. C. Miner, "The Ring Armature Telephone Receiver", Bell System Technical Journal, Vol. 30, pages 110-140 (1951) and in U.S. Pat. No. 2,506,624, "Electroacoustic Transducer", issued May 9, 1950.
While certain ternary Fe-Cr-Co alloys are disclosed in the paper by H. Kaneko et al., "New Ductile Permanent Magnet of Fe-Cr-Co System", AIP Conference Proceedings No. 5, pages 1088-1092 (1972), a number of disclosures are concerned with the presence in the alloy of limited amounts of certain fourth elements. For example, the paper by H. Kaneko et al., "Fe-Cr-Co Permanent Magnet Alloys Containing Silicon", IEEE Transactions on Magnetics, September 1972, pages 347-348, U.S. Pat. No. 3,806,336, "Magnetic Alloys", issued Apr. 23, 1974, and U.S. Pat. No. 3,982,972, "Semihard Magnetic Alloy and a Process for the Production Thereof", issued Sept. 28, 1976 are concerned with properties of alloys containing silicon. The addition of molybdenum as well as the addition of silicon are disclosed in the paper by A. Higuchi et al., "A Processing of Fe-Cr-Co Permanent Magnet Alloy", Proceedings 3rd European Conference on Hard Magnetic Materials, pages 201-204 (1974). The paper by W. Wright et al., "The Effect of Nitrogen on the Structure and Properties of Cr-Fe-Co Permanent Magnet Alloys" and U.S. Pat. No. 3,989,556, "Semihard Magnetic Alloy and a Process for the Production Thereof", issued Nov. 2, 1976 disclose the addition of titanium, the former for the purpose of guarding against a possible adverse influence on magnetic properties due to the presence of dissolved nitrogen and the latter for the purpose of achieving semihard magnetic properties in the alloy. The paper by H. Kaneko et al., "Fe-Cr-Co Permanent Magnet Alloys Containing Nb and Al", IEEE Transactions on Magnetics, Vol. MAG-11, pages 1440-1442 (1975) and U.S. Pat. No. 3,954,519, "Iron-Chromium-Cobalt Spinodal Decomposition Type Magnetic Alloy Comprising Niobium and/or Tantalum", issued May 4, 1976 disclose the addition of alpha-forming elements.
Processing of Fe-Cr-Co alloys typically involves preparing a melt of constituent elements Fe, Cr, Co, and possibly one or several additional elements, casting an ingot from the melt, and thermo-mechanically processing the cast ingot. It is generally recognized that achievement of high coercivity in such alloys is concomitant to the development of a spinodal structure, namely a submicroscopically fine two-phase structure in which an iron-rich phase is interspersed with a chromium-rich phase.
Exemplary thermomechanical processing of alloys containing Fe, Cr, and Co conducive to the development of a spinodal structure is disclosed in U.S. Pat. No. 4,075,437, and may proceed by subjecting an ingot to hot working, quenching, solution annealing, quenching, cold working, and aging. As a result of such processing, applied to an exemplary alloy containing 58.5 weight percent Fe, 26.5 weight percent Cr, 15 weight percent Co, 0.25 weight percent Zr, 1 weight percent Al, and 0.5 weight percent Mn, desirable magnetic and mechanical properties were obtained. Specifically, magnetic properties obtained were a coercivity of 450 Oersted, a remanence of 8300 Gauss, and a usable energy product of 1.6.times. 10.sup.6 Gauss-Oersted.